This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. 2.1 Primary 2.1.1 To determine whether the incidence of acute (preoperative) grade 2-5 gastrointestinal toxicity associated with preoperative chemoradiotherapy is reduced by inverse-planned IMRT-based radiation treatment (when compared with conventionally delivered radiation treatment as was utilized in the capecitabine and oxaliplatin arm of RTOG 0247). 2.2 Secondary 2.2.1 To evaluate the feasibility of performing IMRT in a cooperative group setting for the treatment of rectal cancer. 2.2.2 To estimate the incidence of all toxicity (hematologic and non-hematologic) associated with protocol treatment in the preoperative period, the postoperative period, and overall. 2.2.3 To estimate the pathologic complete response rate following preoperative IMRT-based chemoradiotherapy. 2.2.4 To estimate the time to treatment failure and patterns of failure. 2.2.5 To correlate pre- and post-treatment levels of serum cytokines with symptoms during and pathological outcomes following preoperative chemoradiation therapy for rectal cancer. 2.2.6 To evaluate the rate of abdominoperineal resections (APR).